1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) display in which contrast reduction due to external light is prevented from occurring, and which is suitable for displaying an image that produces a sense of depth.
2. Description of the Related Art
In an organic EL display, an image is displayed by means of spontaneous light which is generated by applying a voltage to a luminescent layer, and therefore is brighter and clearer than that obtained in a liquid crystal display that requires a back light, and not susceptible to a viewing angle. Because of these advantages, attention is focused on an organic EL display as a next-generation display device.
An organic EL display has a standard structure in which a carrier transporting layer 3 and an organic luminescent layer 4 are stacked on a stripe-like transparent electrode 2 on a transparent substrate 1, and a stripe-like back electrode 5 is placed so as to perpendicularly cross the transparent electrode 2. Also a single-layer light emitting device is known in which an electron-injecting layer is additionally deposited on the organic luminescent layer 4 on the side of the back electrode 5, or organic illuminants are dispersed.
When a data signal of a positive voltage and a scan signal of a negative voltage are supplied at independent timings to the transparent substrate 1 and the back electrode 5, holes and electrons are injected into the organic luminescent layer 4 from the transparent electrode 2 and the back electrode 5. In the organic luminescent layer 4, the holes and the electrons are recombined (S) to excite an organic illuminant corresponding to a specific pixel. An object image is displayed by luminescence L transmitted through the transparent substrate 1.
When an image displayed on an organic EL display is observed, also external light reflected by the back electrode 5 simultaneously comes in sight. This mixture of external light which adversely affects the contrast and distinction of a displayed image can be prevented from occurring, by sticking a polarizing plate onto the organic EL display to restrict reflected light of external light. However, this countermeasure requires a polarizing plate that is generally expensive, and therefore the production cost of a resulting organic EL display is high. Moreover, the sticking of a polarizing plate causes the organic EL display to be flattened, and a displayed image tends to become a flat image which scarcely produces a sense of depth.